Abstract: Sensitive skin is a subjective, lay term that many consumers claim affects their comfort when using products that contact their skin. Approximately one-half of individuals surveyed in two research studies considered themselves to have sensitive skin. Researchers know this condition exists, yet it is notoriously difficult to quantify in a meaningful and uniform way.

Sensitive skin is a subjective, lay term that many consumers claim affects their comfort when using products that contact their skin. Approximately one-half of individuals surveyed in two research studies considered themselves to have sensitive skin.1,2 Researchers know this condition exists, yet it is notoriously difficult to quantify in a meaningful and uniform way. Individuals with sensitive skin typically experience a more rapid and intense sensory response to irritating substances than do people with “normal” skin. In some individuals, this response is reported as stinging (see Stingers) and burning. Moreover, in most cases sensory responses to irritation are not accompanied by erythema or other visible signs of irritation.3

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Sensitive skin is a subjective, lay term that many consumers claim affects their comfort when using products that contact their skin. Approximately one-half of individuals surveyed in two research studies considered themselves to have sensitive skin.1,2 Researchers know this condition exists, yet it is notoriously difficult to quantify in a meaningful and uniform way. Individuals with sensitive skin typically experience a more rapid and intense sensory response to irritating substances than do people with “normal” skin. In some individuals, this response is reported as stinging (see Stingers) and burning. Moreover, in most cases sensory responses to irritation are not accompanied by erythema or other visible signs of irritation.3

Nonetheless, manufacturers of consumer products such as lotions, soaps, facial tissues, cosmetics and other toiletries continue to seek greater understanding of sensitive skin and sensory responses to irritating substances. In one study, 78% of consumers who considered their skin to be sensitive reported avoiding some products because they experienced unpleasant sensory effects during a previous use.1

Sensitive Skin Responses to Irritants Research has yielded mixed results about the relationship between subjective sensory response and objective signs of reaction to irritants. A 2005 study evaluated data to determine any correlation between objective scores of erythema and sensory irritation effects reported by participants. The study found a correlation between magnitude of the irritation score (objective) and sensory (subjective) reports of irritation in 13 of 15 participants.4 Another study included participants with sensitive and “normal” skin in the evaluation of facial tissues.5 This study found that the sensory effects were the most reliable indicator of product differences, as opposed to measures of erythema and dryness.

Transepidermal water loss (TEWL) is a biologic endpoint that is an indicator of skin barrier function. Research studies evaluating the association of barrier function and skin sensitivity have shown that a high baseline TEWL was associated with increased sensitivity to a variety of cutaneous irritants using a variety of assessment methods.6

In spite of many inconclusive studies of skin sensory response to irritants, it is known that some individuals have greater sensitivity to irritating substances. Yet, these reactions cannot predict similar reactions to other substances. Sensory reactions to irritants are immediate,7 followed by observable visible signs such as erythema.3

A recent study has proposed that sensory responses to cutaneous irritants may be related to innervation, although more research will be necessary to further evaluate this possibility and to study the role of nerve density variation in the epidermis.8

Host Factors Affecting Sensory Responses
Understanding the complex issue of sensitive skin requires consideration of the various host factors that differ from person to person and between different anatomic sites. Numerous studies have identified differences in skin sensitivity according to factors such as gender, age, race and body site, as well as cultural, environmental, and other factors.

Gender: It is commonly believed that sensitive skin is more common in women than in men. However, one study testing reactivity to 11 different irritants, including sodium lauryl sulfate (SLS), found no differences in skin irritation between men and women.9

Self-reported sensitive skin is especially common among women. Two studies found that a nearly identical percentage of women surveyed on two continents stated that they had sensitive skin-52% in a US study and 51.2% in a UK study.1,2 An epidemiological study conducted in England surveyed men and women to assess the prevalence of sensitive skin and any cosmetic-related adverse reactions.2 The study found that 51.4% of women and 38.2% of men believed they had sensitive skin. It is not known what factors are responsible for these differences, although one study found that the epidermis was thicker among men (p < 0.0001).10 In addition, hormonal differences may cause increased inflammatory sensitivities in women.6 Cultural factors as well as habits and practices, such as practicing fastidious vulvar hygiene cleansing with good intent, are often responsible for irritation.11

Age: There are few documented changes in skin related to aging. Tactile sensitivity, sensory nerve function, and skin innervations have been shown to decrease with advancing age, as did the appearance of visible irritation.9 Younger adults have more sensitive skin than elderly individuals.9 Even though elderly subjects demonstrated less of a reaction to an irritant as opposed to younger subjects, the irritated site required more time to heal.6

Anatomical site: Skin sensitivity varies according to anatomical site. Structurally, the stratum corneum is thickest on the palms and soles, and is thinnest in the region of the genitalia.12 Stratum corneum turnover is 10 days for facial areas13 and is longer12 in other anatomic regions. The nasolabial fold is the most sensitive area of the face8 and the wrist is more sensitive than any other area on the forearm.6 Skin sensitivity of the vulva is a special case (see Skin Sensitivity of the Vulva).

Environmental and Other Factors
Most individuals with sensitive skin experience adverse sensory responses to environmental conditions, such as hot and cold temperatures, wind, sun, and pollutants.1,14 One study6 found that participants exhibited greater irritation from SLS exposure during the winter. Sensitive skin can also be affected by a variety of other factors, such as chemical exposure and home climate characteristics.12 Prolonged use of topical cosmetic/personal care products can lead to irritation of sensitive skin and corticosteroids-containing products used long-term have been shown to result in “fragile” skin.15 Atopic dermatitis, a very common dermatological condition, is thought to possibly predispose individuals to sensitive skin.1,16

Research has shown that there is a positive relationship between atopic dermatitis and the stinging response to irritants.15 Another study found that atopic skin possesses a higher density of cutaneous nerves than normal skin.14 Research has also found that individuals with respiratory atopy and active rhinoconjunctivitis had increased skin response to applied irritants.17 In addition, there may be a connection between rosacea and sensitive skin; 64% of patients with rosacea were also found to be stingers.14

Conclusion
Characteristics of the host are just one collection of factors that contribute to sensitive skin and skin irritation. Future research studying the skin compatibility and safety of products that contact the skin will continue to seek answers to the unknown relationships between sensitive skin, sensory responses, and objective evidence of irritation.

This is the concluding article in a three-part series on the Sensitive Skin Syndrome. The first article in the series discussed sensory response and classification.18 The second article discussed the relationship between irritant stimulation and sensory response.19 Also of interest is Reference 20, which summarizes much of the relevant literature. In spite of considerable progress, much remains to be done before the needs of the consumer are requited.

Acknowledgments: The authors acknowledge the kind permission from Blackwell Publishing allowing this article to republish parts of the following original publication: MA Farage, A Katsarou and HI Maibach, Sensory, clinical and physiological factors in sensitive skin: A review, Contact Dermatitis 55(1) 1–14 (2006).

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Stingers

Among sensitive skin individuals, there is a subgroup known as stingers, so named because in response to chemical irritants, they experience unusually strong sensations of stinging and burning. Beyond subjective sensory responses to irritants, some stingers also exhibit greater erythematous (objective) responses to irritant exposure.

Early research in 1977 on this subject found that stingers had heightened susceptibility to general irritation.21 However, more recent studies22,23 found no evidence that strong reactivity to one nonimmunological irritant was predictive of such a response to other irritants.22

Evaluating Skin Sensitivity of the Vulva

Studies of skin sensitivity utilizing irritants may be conducted on exposed or partially occluded skin. The characteristics of the vulva differ greatly when compared to exposed skin. In contrast to exposed skin, the vulva is considered occluded tissue, and it also has increased hydration,11 more hair follicles, sweat glands and increased blood flow.10

The current authors recently found that individuals with vulvar erythema at study enrollment also reported significantly more facial erythema resulting from a topical product.24 In many cases, sensitivity in the vulvar region may result from overuse of topical hygienic and medicinal preparations.25 Safety testing of feminine hygiene products considers the potentially higher permeability of vulvar skin and increased secondary sensitization.10

The best method of evaluating vulvar sensitivity to irritation utilizes the combined methods of assessing blood flow, pH and color reflectance.16